Electronic delay system



June 3, 1952 J. P. SMITH 2,599,206

ELECTRONIC DELAY SYSTEM Filed Dec. 24, 1948 2 SHEETS-SHEET 1 June 3, 1952 l J, P. sm., y 2,599,206

ELECTRONIC DELAY SYSTB Filed Dec. 24, 1948 2 SHEETS-SHEET 2 Gttorneg Patented June 3, 1952 ELECTRONIC DELAY SYSTEM John Paul Smith, Granbury, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 24, 1948, Serial No. 67,157

8 Claims. (Cl. Z50-27) This invention relates to improved apparatus.

for delaying a continuous signal or a complex wave. More specifically, the invention relates to a delay device for Waves in the audio band (maximum frequency about kc.) utilizing two single gun storage tubes and circular scanning. The present invention is related to co-pending application, Serial No. 18,119, of Max H. Mesner, filed March 31, 1948-, PatentNo. 2,579,269 issued December 18, 1951.

In the past, delay networks, as well as other delay devices, have been used to delay audio frequency signals for a desired period of time. However, networks for delaying complex waves for periods of time intended to be covered by the apparatus of the present invention are usually complicated and diiiicult to construct. In the present invention, a circuit is provided in which two single gun storage tubes, `such as those known as the RCA SDT-5, or the signal plate kinescope may be used to obtain a delay of a signal, one of the tubes delaying information received during one interval of predetermined length and the second tube delaying information received during the next succeeding interval while the first information is being reproduced. In the present invention, circular scanning is used on both tubes. The delay time may be varied over a wide range up to about 3,000 microseconds, using two tubes.

One object of the present invention is to provide an improved apparatus for delaying an audio frequency signal for a predetermined interval of time.

Another object of the invention is to provide an improved acoustic delay apparatus in Vwhich substantially none of the signal is lost.

Another object of the invention is to provide an improved acoustic delay apparatus utilizing a plurality of single gun storage tubes and circular scanning.

Another object of the invention is to provide an improved acoustic delay apparatus utilizing storage tubes and a scanning system with maximum resolution.

Another object of the invention is to provide an improved acoustic delay system utilizing storage tubes and a scanning system requiring no blanking of return lines.

These and other objects will be morev apparent and the invention will be more readily understood from the following specification and the accompanying drawings, of which:

Fig. 1 is a block diagram of one embodimen of the present invention,

Fig. 2 is a schematic diagram of a preferred form of a partial circuit which'may be used in the system shown in the block diagram of Fig. 1, and

Fig. 3 is a graphical illustration of wave forms appearing in different parts of the system shown in Fig. 1.

Referring now to Fig. 1, a sine wave oscillator 2 supplies a sine Wave output, the frequency of which is selected so as to obtain a desired delay interval. The length of the delay interval will be equal to the time length of one complete cycle. Therefore, to obtain, say, a continuous delay of 3,000 microseconds, an oscillator frequency of 333.3 cycles per second would be used. A resistor control 4 may be used to vary the frequency of the oscillator. This oscillator may be any one of many known conventional types. An example of one suitable type is described in Proceedings, I. R. E., volume 29, page 43, 1941.

Part of the output of the oscillator 2 is fed to a phase shifter B. The sine output 8 of the phase shifter is fed to the horizontal deflection coils I0 and I 2 lof the deflection yokes of storage tubes No. I and No. 2, respectively, While the cosine output is fed to the vertical deection coils I4 and I6 of these two tubes. The two windings of the yoke are electrical degrees apart.

The phase shifter is controlled through a variable resistor I8 which is adjusted to obtain 90 phase shift of the sine wave output with respect to the cosine wave output and thus produce circular scanning of the screens of the storage tubes. Many different, well known types of phase shifter are suitable for this purpose, one of them being described in the General Electric Review, July 1929, page 394. When the sine wave oscillator frequency is changed to obtain a different delay period, the phase shift control is also varied to get the required 90 shift unless a wide band phase shifter is used.

Another part of the output of the sine wave oscillator 2 is fed to an f/2 frequency divider 20 which halves the output frequency, thus doubling the time interval of each oscillation. Forexample, if the sine wave oscillator 2 produces sine waves, each cycle of which are 94,33 second long, the length of each cycle of the output wave of the frequency divider will be 2/333 second long. This frequency divider may be of the type shown in the Bell Laboratories Record, December 1942, page 99. The purpose of the frequency divider is to permit information to be stored on each tube for 1/2 .of `each of the longer period cycles. Onehalf of each of the longer period cycles corresponds to the entire length of each of the original cycles. The above mentioned type of frequency divider is but one of many different types which can be used in the present invention.

The output of the frequency divider is fed to a clipping circuit 22 which produces a square wave output having the same frequency as that of the frequency divider. This clipping circuit may be of the type described in U. S. Patent 2,132,655 of J. P. Smith. Other conventional types of clipping circuits may also be used.

The square wave output of the clipping circuit 22 is then fed to a diierentiating circuit 24. The differentiating circuit passes only the high frequency components of the square wave. The high frequency components are represented by the steep sides of the Vsquare wave while the tops of these Waves represent the low frequencies. Hence, the output of the differentiating circuit is a series of pips or pulses of very short duration, say l microsecond. V'These pulses occur at the beginning-and end of vleach half cycle of the square Wave fand, therefore, have a frequency the same as that of the original output of the sine wave oscillator 2. A .suitable differentiating circuit is also shown'in theabovementioned Smith patent.

Part of the output of the differentiating circuit 2i41is applied 'to .a polarity reversing circuit 26 of any vconventional type,'which may include an amplier. The polarityireverser reverses the plarityof the pulse output of the diierentiator and aplies this output to each'of two trigger tubes `A andD, which control the input of storage tube No. I and the' output of storagetube No.2, respectively. Another part of the output of the diiferentiator 24 'is fed, without polarity reversal,

to two `other .triggerr tubes Band C which con-Y trol the'inputo'fLstorage tube No. 2 and routput of'storaget'ube No. `I, respectively.

Theaudio input signal from' a source (not shown), which is to be .delayed by the .selected predetermined time interval, is divided and fed in parallel lto 'trigger tube A controlling the input of lstorage tubNo. Land to the trigger tube C which controls'the input of storage tube No. 2. All trigger 'tubes'fare turned on' by positivefpulses and Vturned oiffbynegativepulses.

Referi'rfgiow toFig 3, as the apparatus is rst pntnfoperaun at the beginning o'f time interval rifwniiet'apositiveipuise bev appiied from the output ofdiiferenti'ator 24 to the trigger rtubes B and C. Thisfp'ermits the audio input signal to be' 'passed through trigger tube C and driver amplifier 28"to` storagetube No. 2.' During this interval,"-then, Aaudio signals are stored on the storage elements fof -tube'No.`4 2. Since a positive pulse is'alscl applied simultaneously to trigger tube B, `information `rwould normally be taken from the cll'ector'electrode dfstorage tubeNo. tand-'passed to the delay audiooutput. However, when the apparatus is irs'tfset'inoperation, noinformation is initiallystored on s'toiage'tube No, landf'therefre, -no delayed audio output appears during this time intervall liAlso, 'at'the beginning'f time interval t1 to t2, a negative 'pulse'fromfthe 'output' of polarity reverser v26"is4 applied totrigger tubes A and D. These' two tubes' are, therefore, cut off and, duriirgtim'e-V interval ti `to te, no audio input is applied'tofstorage tube No.- I and no output is taken from stoagetbe'Ndf 2.

'.At thebeginning of. time :interval tz toV t3, a negative .pulse is applied 'to trigger .tubes i B and C arid apositivepulseiisA applied totrigger .tubes A 'and 1D. lDuring this'timeinterval,"therefore,

there is no audio output from storage tube No. I; audio input is applied through driver amplifier 30 to storage tube No. l and the information stored on storage tube No. 2 during the preceding interval ti--t2 is read oi and appears as the delayed audio output.

At the beginning of time interval t3 to t4, a positive pulse is applied to trigger tubes B and C and a negative pulse is applied to trigger tubes A and D. During this time interval, audio input signal is again stored on storage tube No. 2 while the information stored on storage tube No. I during the preceding interval appears as the delayedfaudio output.

This Atype of operation is repeated during succeeding time intervals such that each part of .the audio inputis delayed by the selected time interval, which interval may be varied by changing the frequency of the sine wave oscillator.

In order to apply audio input signal alternately to each of the storage tubes and lthen'read'off the ystored signal first .from one tube, then the other, a suitable switching circuit is necessary.

An electronic reversing switch is preferred Which will connect and disconnect circuits Without putting 1in transients. Or, if some transients are introduced, they should be of such high frequencies as .to enable them to .be filtered out, vas by a yconventional filter circuit 32, without appreciably aiecting the 15 kc. components of the signal.

In Fig. y2,*there is illustrated ,a preferred form of switching circuit which maybe made tohave switching times of l microsecond or less. There are four identical .circuits of this itype, two of which control theinput and output of storage tube No. I and .the other two of which vcontrol the input andoutput of storage tubeNojZ. :Each of these circuits `includes a secondary emission trigger type tube A, B, CY or D, such as described in the VBell Laboratories Record,`April 1943, pages 233-236. This -is a` vacuum .tube which maybe turned on and off with apulse having a `time duration `of the order of 1 microsecond. Each tube has a cathode, a control grid, a iirstanode having an opening for .thepassage of electrons, a reflector, an anode screen and a second anode. If the grid is made positive, some Tof the electrons now fromthe cathode throughthe opening in the first anode to the reflector which deiiects the path Vof the -electronsso thatthey strike the second anode. 'The second. anode Yemits .secondary electronsl which vare .collected by a collector grid. Control grid bias is supplied to thel control grid of eachtube by'means f grid biasing resistors 34, 38, 38 :and 40, respectively, which are connected through .the secondaries. of audio input transformers 42, '.44, 46 .and 48, respectively,'.by means oflwh'ichtransformers audio'input signal is alsoappliedto thecontrolrgrids ofeachxofthe triggertubes.

The first anodeof each .of the :trigger tubes is supplied with al positivezpotential from asuitable source such asa battery. Each of .these lanodes is also connected to the primary ofanzaudio. output transformer 50, .752, 54 .or i518. "The second anode of each tube 'is supplied with an adjusted potential from .one ofthe resistors 34, 36, 38 Ior `40, which also serve y as" grid-biasing resistors. The collector grid of each tubev may be connected to the saine source of positive potential .as .is con-.- nected to the secondY anode.

There are two Apotentials,"a'ilower o nelof jwhich may be'called A`.a.nd.an. upper'nne of whichgmay be called "B at which the ".Cllrreiltf 13.0. the. 5.89011@ anode is'zero in this type of tube. I'he B potential is a stable condition resisting any attempt to change it. At the A potential, however, the application of even a slight positive pulse to the second anode causes its potential to jump to the B condition at which the tube amplies as an ordinary triode. As the potential of the second anode is raised, the grid is driven a volt or two in the positive direction by the potential so that a small amount of electron current begins to now in the tube. The sudden jump of the potential of the second anode to the B condition carries the potential of the grid to its operating potential. The tube is now in the on condition and can be used to amplify the audio input signal.

The tube may be returned. to the olf condition by momentarily applying a negative pulse to the second anode. The negative pulse should be sucient to drop the potential on the second anode to just below the A condition.

The 1 microsecond spikes occurring in the delayed audio output may be :filtered out by the conventional filter 32 without appreciably affecting the 15 kc. components.

The audio input signal passed by trigger tubes A or C passes through audio output transformers 50 or 54, respectively, to driver amplifier tubes 58` or 60. These tubes each have anode biasing resistors 62 and 64 and cathode biasing resistors 66 and '68, respectively.

The amplied audio input signals are applied to the signal plates of the storage tubes alternately. These tubes are preferably of a type known as RCA SDT-5, a description of which, together with the mode of operation, appears in anY article entitled The Barrier Grid Storage Tube and Its Operation, Smith, Mesner, Flory and Jensen, RCA Review, March, 1948, volume 9, No. 1. This tube was also described in U. S. Patent 2,433,941. The tube includes an evacuated envelope containing a heated cathode at one end. Surrounding the cathode are grids, each of which is provided with an orifice for the passage of electrons supplied by the cathode. In front of the grid structure, there is positioned a collecting electrode or l2. An accelerating anode is present as a metallic coating on the walls of the tube between the collecting electrode and the signal plate. The signal plate consists of a front and a rear portion. The front portion faces the source of electrons and may be a dielectric coating such as aluminum oxide. is a metallic plate usually made of aluminum. Immediately in front of the front surface of the signal plate is a metallic screen of fine mesh which is grounded.

The general operation of the tube is as follows. The beam of electrons from the cathode passes through the ne mesh screen striking the dielectric target side of the signal plate at high velocity. Secondary electrons are emitted from the dielectric surface and, if the bombarded area is negative relative to the screen, pass through the screen towards the output or collector electrode. This causes the bombarded area of the target to become more positive, until the potential of the bombarded target area reaches that of the screen. If the bombarded area of the target is positive relative the the screen, the secondary emission from the area is suppressed by the negative eld caused by the screen and the target element becomes more negative until it reaches screen potential. When no signal is being impressed on the signal plate from a signal source during the The rear portion the target brings the scanned areas to the poteni tial of the screen. The beam is made to have suicient intensity to substantially instantly bring the potential of an elemental area to the screen potential.

In the present invention, the dielectric side of the signal plate of each tube is continuously scanned by a beam of electrons in a circular manner, as previously explained. During the time interval, t1 to t2, the audio input signal modulates the signal plate of storage tube No. 2 and each elemental area struck by the electron beam is brought to and left at a potential which is directly proportional to the voltage level of-the modulating signal.

During the next time interval, t2 to t3, the audio input signal is similarly stored on the signal plate of storage tube No. l. During this time interval, also, the signal previously stored on the plate of storage tube No. 2 is read off. This is done by again scanning the coated target side of the signal plate. During this scansion, the number of secondary electrons leaving each elemental area is proportional to the potential at which the area was left by the previous scansion. The secondary electrons travel to the collecting electrode l2 and the original audio input signal is thus reproduced in the output of the tube.

The signal output of storage tube No. l is taken from its collecting electrode 10, applied to audio input transformer 44, passed through' switching tube B and thence applied by audio output transformer 52 to the delayed output portion of the circuit. The microsecond switching pluses may be ltered out by a convention filtering circuit. 32 comprising a suitable resistance 14 and capacitance 'I6 before being utilized.

Similarly, the signal output of storage tube N 2 is applied through audio input transformer 48. switching tube D and audio output transformer 56 to the delayed audio output circuit.

There has thus been described an improvced acoustic delay system in which many of the shortcomings of previous systems are eliminated. Circular scanning, for example, permits greater resolution than linear scanning since the scanning path is about 3.14 n times kas long as one line in linear scanning. N o blanking of return lines is necessary as in a system using television roster scanning because there are no retur'n lines. When sawtooth scanning is used, blanking of the return lines is usually required and the blanking signals normally appear in the output unless eliminated in some manner. inated completely, gaps will appear in the delayed output signal.

Systems other than the one described may be used for obtaining circular scanning. One set of yoke coils may be tuned to 70% amplitude on one side of resonance and the other set to 70% amplitude on the other side of resonance. Phase shifting could also be accomplished by means of and oi in the proper order but the switching means could be of the same type as described above and circular scanning would be accomplished simultaneously in all tubes in exactly the same manner as when only two storage tubes are Even if elim- 7 used. Input. signal would. be.: placed O11 the' Sig.- nal: plate of. each storage` tube in turn.A in some predetermined; order and then read off againin the. sameorder. Qutputs of all storagev tubes could.- be.` combined inV a single. delayed output.

with. a. beam. of electrons at said predetermined.

energy: level, means forl repeatedly modulating the input signalapplied to. each of. saidelectrodes in. a. predetermined orderv whereby successive portions; of: said signal; are stored on: diierent signal plate', electrodes, andmeans, including said electron. bea1n,. for removingI said signal portions in the same order after; a. time delay equal to said; predetermined. period..

2. Apparatus according'. to claim'4 1 includingv means.Y for. recombining said delayedv signalpor tions to; form a continuous'. signal.

Apparatus. forV delaying an input. signal.. for

a. predetermined period of time before applying. said'. signal to, aA utilization circuit comprising, a.

first" and. a. second storage tube each having a signal plate electrodeY ofi which each. elemental,

areais; capable of. temporarily storing a.. charge havingf a potential proportional to a modulating input signal voltage. applied to. said; electrode, when saidV area. is-v` struck. by a beamV of.v electrons off predetermined. energy level,rmeans for circularly scanning eachof said electrodes simultaneously with a` beam of electrons at. saidv prede.- termined energy level and at, a.v frequency such that each. cycle is equal. in length to said. delay period, means for alternately modulating; the inputJ signal applied to saidplates', at. alfieriodic.m ity equal. to. the length. of each of said cycles, whereby successive. portions. of; said. signal are.

stored on. one. of. said electrodes andi then. thev other', and means. for removing said, signalportions alternately from said.r electrodes after a time. delay periodequal to said predetermined.

period 4. Apparatus according to claim. 3 inA which saidgscanning frequency isVcontrol-led by a sine WaveI oscillator and including means for conf trolling the alternate application of said signal to said .signal plate electrodes withvoltage pulses derivedfrom the output of said oscillator.

5. Apparatus for delaying an'input signal for a predetermined period. of time. before applying-said signal to a utilizationl circuit, comprising a first and a second storage tube each having a storage electrode of which each elemental area is capable of temporarily storing a charge having a. potential proportional to a modulating input signal Voltage. applied to said electrode, when said area is struck by a beam of electrons of prede-- termined energy. level, means for ci-rcularly scanning each of said electrodes.simultaneously with a beam of electrons. at said energy level andvat a frequency such. that the. time between succes-l sivescans is equal to said delay period, means for applying an audio frequency input. signaltofsaid. electrodes, meansV for switching said input alternately between electrodes, means for removing; the signall stored on one of saidelectrodes) while. signal is'being storedon the other, andmeans fon combining bothl parts of said signal in an output circuit.

6; Apparatus according to claim- 5 in which.. said switching means is a. vacuum tube-whichL is rendered instantaneous-lyconductive. by the appli cation thereto of energy pulses having a dura.- tion of the order ofl microsecond.

7.'. Apparatus for delaying an input signal for a. predetermined period of time. before applying. said signal to a utilization circuit, comprising. means for generating a continuous series of Waves Vhavinga` frequency suchk that each cycleA has; a

length equal to said delay period, meansfordef drivingl pulses of energy alternately positive; and negative from said Waves, the frequency of said pulses being equal. to the frequency of said Waves, a first and a second storage tube each having.' a storage electrode of whichl eachelemental area is capable of temporarily storing a chargez having a potential proportional; to a modulating input signal voltageV applied to said electrode.. when said area is struck by a beam ot electrons. of predetermined energy level,. means for -circularly scanning each of said electrodes, simultaneous--` ly and out of phase, with a beam ofelectrons at said energy level and at a frequency equal: to-the frequency of said waves, means for simultaneously controlling the signal input of said second` storage tube and the signal output off said-l first storage tube, said last mentioned means being'v responsive to said positive and negative energy pulses, meansfor reversing the polarityot apart of the output of said pulse deriving means, meansresponsive to said pulses of. reversedl polarity for' simultaneously controlling the signal input of said first storage tubel and the signal outputr of said second storage tube, means for applying an audio input. signal to said storage electrodes. through said signal input controlling meanstand means for taking off said signal from saidstorage electrodes through said output controllingfmeans.

8; Apparatus according to claim 7 in which saidv wavegeneratingY means is a Variable frequency oscilla-tor.

JOHN PAUL SMITH.

REFERENCES CITED Thefollowing references are of record in the.

tile of thispatent:

OTHER REFERENCES Electronics Magazine Reference, September 1.947, volume 2D, pages 80783, .A.Memory Tube by Haeif.. 

